1. Field of the Invention
The present invention is directed to the field of automotive headlamp systems and more specifically to the area of automatic control for such systems in order to down-switch the beam patterns and prevent interfering glare to oncoming drivers.
2. Description of the Prior Art
In U.S. Pat. Nos. 3,373,311 and 3,894,227 inventions are disclosed which provide "tri-beam" headlighting systems of low, mid and high beam patterns controlled by various manually actuated switches to obtain the appropriate selection.
Low-beam headlamps are designed to provide adequate illumination for a vehicle operator without producing unacceptable glare for operators of opposing or oncoming vehicles. The low-beams are directed so that the high intensity projection areas of its beam patterns are directed sightly down and to the right for countries of the world which utilize right hand traffic patterns. In left hand traffic patterns, the low-beams are aimed down and slightly to the left. (For the remainder of this discussion right hand traffic patterns will be assumed.) With the use of low-beams, the left lane, the mid foreground and the right lane, beyond approximately 150 feet, are not intensely lighted. On the other hand, high-beam patterns are generally directed so as to cover much wider horizontal and vertical angles that will cause glare in the eyes of drivers of oncoming vehicles even on straight roads.
The mid-beam concept, although first disclosed several years ago, provides more usable light directed to the right edge of the driving lane without causing increased glare to opposing drivers, while on straight roads. However, the mid-beam concept has not been adopted by the industry. It is believed this reluctance to adopt such an improvement in headlighting systems is based upon the fact that when a mid-beam system is utilized, there are still those instances when the mid-beams have to be down-switched to the low-beams in order to prevent glare from interfering with the vision of the oncoming driver. For instance, when the road geometry varies (curves and hills) or the lamps are misaimed so that they could cause the high intensity projection areas of the mid-beam pattern to be directly aimed at opposing drivers, down-switching of the lights is required. Taking into consideration the aforementioned patents it is believed that such systems of manually down-switching from mid to low-beams by a vehicle operator would require the operator to have a sophisticated understanding of the system concepts in order to appreciate the necessity of when to manually down-switch the beams. It is clearly evident that a manually controlled mid-beam system is not practical, since it has not been adopted by the industry. Applicants have appreciated that it would be desirable to have an automatic headlamp control system, but such control systems presently available for high-beam down-switching will not function for a "tri-beam" headlighting system. U.S. Pat. Nos. 3,177,397; 4,599,544; and 4,645,975 are typical of such high-beam control systems.